posted by Anonymous .
A straight river flows at a speed of 20km/h. A boater starts at the south shore and heads in ths direction of 70degrees from the shore. The boat has a speed of 20km/h in still water. Find the true speed and direction of the boat.
Let the river flow in the +x direction.
Across the river is then +y.
river velocity = (20,0)
boat velocity relative to the water
= (20cos70°,20sin70°) = (6.84,18.79)
resultant velocity relative to land
speed: √(26.8^2+18.79^2) = 32.73
tanθ = y/x = 18.79/26.84 = .70
θ = 35°